1. Field of Invention
The present invention relates to a method for improving a vacuum, more particularly, to a method for achieving high vacuum of a vacuum display.
2. Related Art
The vacuum of an ordinary vacuum display may significantly affect the service lifetime and display quality of the vacuum display. For example, the interior of a Field Emission Display (FED) is a vacuum the same as a cathode ray tube (CRT), and the FED operates under a high vacuum state of 10−7 Torr to avoid electrons bumping against gas which may cause an effect similar to plasma or glitter and damage inner elements. Therefore, a pumping pipe is left in the FED having its upper and lower panels packaged, for vacuum pumping.
Use of the FED accomplishes the planarization of the CRT. The weight of the FED is less than a tenth that of the CRT, and the thickness of the FED is only a tenth that of the CRT. The power consumption of the FED is also lower than that of other types of display devices, and it eliminates the problem of view angle existing in the liquid crystal display (LCD). Therefore, the FED has enormous potential to meet demands for planarization, high luminance, and light weight.
The display method of the FED is similar to the operational principle of the CRT. That is, electrons are emitted from a cathode, pass through the vacuum, and are accelerated by an anode, thus bumping against the fluorescent material to emit lights. The fluorescent materials for both FED and CRT are the same, and the difference resides only in the way of generating electrons. In the CRT, the electrons are generated by heating the cathode tube, and are usually called hot cathode electrons, while in the FED, the electrons are drawn from the cathode with an electric field, and are usually called cold cathode electrons.
The internal circuit and carbon nano-tube in the FED have many holes for trapping gas molecules, i.e. reserving gas. When vacuum pumping, the whole FED is heated, such that the gas molecules acquire kinetic energy to dissociate from the surface, so as to purge gas adsorbed on the glass or other elements in the space, and exhaust the gas with a vacuum pump. After vacuum pumping, the pumping pipe is closed, sealed, and severed by heating with an oxyhydrogen flame gun, thus finishing packaging of the FED. After finishing packaging, there is still some residual gas in the FED and at this time the vacuum still cannot reach 10−7 Torr. Therefore, before packaging the upper and lower panels, a getter is placed therein, and after the pumping pipe is sealed, the getter is heated with high cycle waves to absorb the residual gas, such that the vacuum reaches 10−7 Torr.
However, for vacuum pumping, the FED usually is heated to above 300° C., such that the FED goes through another thermal cycle and thermal expansion and contraction. The inner elements and materials may be degraded when heating. And the glass panel may have a certain residual stress, and will be broken under a slight force. Therefore, both the product rate and service time of the FED are affected.